title: Tryptophan 46 is a site for ethanol and ivermectin action in P2X4 receptors.
abstract: ATP-gated purinergic P2X4 receptors (P2X4Rs) are the most alcohol-sensitive P2XR subtype. We recently reported that ivermectin (IVM), an antiparasitic used in animals and humans, antagonized ethanol inhibition of P2X4Rs. Furthermore, IVM reduced ethanol intake in mice. The first molecular model of the rat P2X4R, built onto the X-ray crystal structure of zebrafish P2X4R, revealed an action pocket for both ethanol and IVM formed by Asp331, Met336 in TM2 and Trp46, and Trp50 in TM1 segments. The role of Asp331 and Met336 was experimentally confirmed. The present study tested the hypothesis that Trp46 plays a role in ethanol and IVM modulation of P2X4Rs. Trp46 was mutated to residues with different physicochemical properties and the resultant mutants tested for ethanol and IVM responses using Xenopus oocyte expression system and two-electrode voltage clamp. Nonaromatic substitutions at position 46 reduced ethanol inhibition at higher concentrations and switched IVM potentiation to inhibition. Simultaneous substitution of alanine at positions Trp46 and Met336 also resulted in similar changes in ethanol and IVM responses. Furthermore, a new molecular model based on the open pore conformation of zebrafish P2X4R suggested a role for Tyr42 that was further supported experimentally. Our previous and current findings, combined with our preliminary evidence of increased ethanol consumption in P2X4R knockout mice, suggest that the ethanol and IVM action pocket in P2X4Rs formed by positions 42, 46, 331, and 336 presents a potential target for medication development for alcohol use disorders.
authors.affiliation: Alcohol and Brain Research Laboratories, Titus Family Department of Clinical Pharmacy & Pharmaceutical Economics and Policy, School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA, 90089, USA.
authors.forename: Maya
authors.initials: M
authors.lastname: Popova
authors.forename: James
authors.initials: J
authors.lastname: Trudell
authors.forename: Kaixun
authors.initials: K
authors.lastname: Li
authors.forename: Ronald
authors.initials: R
authors.lastname: Alkana
authors.forename: Daryl
authors.initials: D
authors.lastname: Davies
authors.forename: Liana
authors.initials: L
authors.lastname: Asatryan
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D003198:Computer Simulation; D000431:Ethanol / Q000737:chemistry* / Q000378:metabolism*; D007559:Ivermectin / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D058848:Receptors, Purinergic P2X4 / Q000737:chemistry* / Q000378:metabolism*; D014364:Tryptophan / Q000737:chemistry* / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D058848:Receptors, Purinergic P2X4; D000431:Ethanol; D007559:Ivermectin; D014364:Tryptophan